1. Field of the Invention
The present invention pertains to copper complexes of amino-functional organosilicon compounds formed by reaction of the amino-functional organosilicon compound with copper(II) compounds. The resulting complexes are heat stable and may be employed to impart heat stability to organopolysiloxanes and other polymers.
2. Background Art
Organosilicon compounds, for example organosilanes, and in particular, polyorganosiloxanes, both linear and crosslinked, have numerous uses. Polyorganosiloxane fluids are often used as mold releases, as heat transfer oils, as lubricants, and as fuser oils in xerographic copying, for instance. Highly crosslinked organopolysiloxanes, in the form of silicone resins, are useful, inter alia, as powder coatings, components of paints and lacquers, and as molding resins. Crosslinked organopolysiloxanes in the form of silicone plastics and elastomers are useful in providing flexible molds, toner and fuser rolls for xerographic copying, rollers for conveyors and the like, and as sealants, encapsulants, and gasketing materials. Organosilanes are frequently used in the preparation and modification of organopolysiloxanes, as well as the modification of numerous other polymers, and for silanization of other substrates such as fillers, paper, textiles, etc. The uses described above are but a very small subset of uses for organopolysiloxanes and organosilanes.
Many of the uses of organosilicon compounds require thermal and oxidative stability for extended periods of time. This is particularly the case where extended exposure to high temperatures is required, for example in heat transfer oils, fuser rolls, fuser fluids, and the like, where temperatures up to 400° F. (ca. 200° C.) or higher may be commonplace.
In xerographic printers and copiers, for example, a fusible toner is electrostatically attracted to an imaging drum and transferred to a substrate, e.g. paper. The paper with toner passes through heated, abhesive rollers to melt the toner and facilitate its adherence onto the substrate and migration into the substrate to prepare a desirable image. The toner must not adhere to the fusing rollers, as otherwise subsequent images would bear some remnant of the preceding image. For this reason, abhesive polymers such as polyvinylidene fluorides, polytetrafluoroethylenes, and crosslinked silicone elastomers have been used in such applications.
Rollers of silicone are very commonplace, and are often fabricated to contain so-called “fuser oils,” often polydimethylsiloxane fluids, to aid in their abhesive nature. These oils are physically incorporated, and slowly exude. The fuser oils may also be applied sporadically to the rollers in lieu of or in addition to being physically incorporated. Aminoalkyl-functional silicone fluids have proven to be especially advantageous, as also have mercaptoalkyl-functional silicone fluids.
While silicones such as polydimethylsiloxanes and poly(methylphenyl)siloxanes are among the most thermally stable polymers, their continued use at high temperatures causes even these polymers to alter their properties over time. For example, as disclosed in U.S. Pat. No. 4,777,087, which also contains a useful description of xerographic processes, the toughness of a silicone roller decreases by about half after 8,000 to 32,000 copies at fusing temperatures near 200° C. The hardness of the rollers increases, and cracks, pits, and eventually fracture of the roller can occur. The roller thus must be replaced after a defined duty cycle. These same problems can occur in silicone elastomers used in other fields, and in other polymers as well.
Many attempts have been used to stabilize silicone rollers against thermal degradation. In U.S. Pat. Nos. 4,777,087 and 4,925,895 for example, a complex of a transition metal salt with at least one polydentate chelating ligand is milled as a solid into one component of a two-component curable silicone composition also containing a silicone fuser fluid, which is then molded to form a roller body. However, this process requires milling the complex uniformly into the uncured composition, and while being a distinct improvement, still has less thermal stability than desired.
An additional problem encountered in xerographic copying is the generation of formaldehyde by decomposition, primarily from the fuser oil. Thus, U.S. Pat. No. 5,395,725 applies fuser oil directly to the fuser roll surface, the fuser oil containing at least one mercaptoalkyl-functional silicone and at least one aminoalkyl-functional silicone. U.S. Pat. No. 5,493,376 employs a fuser oil containing a silicone fluid and a thermal stabilizer which is a reaction product of chloroplatinic acid and a cyclic polysiloxane or a linear polysiloxane containing at least one unsaturated group. U.S. Pat. No. 5,864,740 is similar, but the stabilizer is the reaction product of a platinum group metal other than platinum, in particular a ruthenium compound, with a polyorganosiloxane. The use of expensive platinum group metals substantially increases cost.
In U.S. Pat. No. 5,604,039, fuser oils with increased thermal stability are prepared from a blend of polyorganosiloxane fluid and a phenol-functionalized polyorganosiloxane fluid, while U.S. Pat. No. 5,780,454 to the same inventor proposes the use of a blend of a conventional polyorganosiloxane fluid, a polyoxyalkylene ether-functionalized polyorganosiloxane fluid, and an antioxidant. U.S. Pat. No. 5,625,025 discloses temperature resistant oils for fuser oil applications as well as other applications such as high temperature lubricants and mold release agents. The compositions contain both amino-functional and phenol-functional diorganopolysiloxane fluids. In U.S. Pat. No. 6,045,961, fuser oils containing polyorganosiloxanes and a stabilizer which is the reaction product of a metal acetylacetonate with both linear and cyclic silicone fluids, each containing an unsaturated group. In columns 1-9 of the U.S. Pat. No. 6,045,961 patent, prior art attempts to obtain thermal stability are thoroughly discussed, as is also the long felt need for still further improvement.
It would be desirable to provide organosilicon compositions which exhibit high thermal stability without the need to mill in solid stabilizers, and which can function without the use of the very expensive metals of the platinum group as stabilizers. It would be further desirable to be able to provide such organosilicon compounds through an economical process with cost-effective ingredients.